Neutralizing system



Feb. 15, 1927.

' R. M. WISE NEUTRALIZING SYSTEM Filed Dec. 22, 1925 INYENTUR By Pager A4. VV/ae ATTo/msrs Patented Feb. 15, 1927.

CUNITED STATES 1,617,733 PATENT OFFICE.

ROGER M. WISE, OF OAKLAND, CALIFORNIA, ASSIGNOR TO E; '1. CUNNINGHAM, OF

. SAN FRANCISCO, CALIFORNIA.

NEUTRALIZING SYSTEM.

Application filed December 22, 1925. Serial No. 76,9 81.

This-invention relates to radio receiving and amplifying systems and particularly to an arrangement for controlling oscillations in systems which employ a plurality of electron emission v tubes coupled together in cascade. In such systemsthere is always a certain amount of energy exchange or feed-back from the output to the input circuit of the respective tubes caused by internal tube capacitance and magnetic interlinkage between the coupling devices, thus causing 0bjectionable local oscillations or howling,

In the past it has been proposed to neu tralize this feed-back coupling by impressing a potential upon the grid which is equaland opposed to the potential imposed by the objectionable feed-back, thus cancelling its efiect upon the circuit. Another arrangement secures neutralization by a reverse feedback of an amount of energy which is equal and opposed to the undesired feed-back. In both of these systems it is impossible as a practical matter to secure perfect neutralization over a substantial frequency range.

Theoretical computations are upset by magnetic interlinkage between the. inductive transformers employed to couple together the tubes and because of capacity effects between the conductors. As. aresult such a system may be neutralized for one frequency but will oscillate locally when tuned to another frequency.

It is an object of this Invention to devise an electron emission tube system in which neutralization of undesired feed-hack energy is secured for the entire frequency range for which the system is :ltltl] )t0(l.5--

It-is a further object ofi'this invention to secure neutralization of undesiredfeed-back energy in a system employing an electron emission tube having an input circuit and an output circuit inductively coupled to another circuit, by means including an inductance.

tron emission tube to neutralize undesired energy feed-back between the output and the input circuits of the tube by the use of a trans former having a primary inductance electrically associated with the output circuit and a secondary coil electrically associated with the input circuit.

It is a further object of this invention to devise a novel method of neutralizing to pre vent local oscillations in an electron emission tube system.

Further objects of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail, it being understood that the invention is only to be limited as defined by the appended claims.

The single figure of the drawings is a circuit diagram illustrating the system of this invention.

.The system has been shown as applied. to a plurality of electron emisson tubes 10 and 11 which in, the particular instance are adapted to amplify electrical energy of radio frequency. The tube 10 is provided with an input circuit 12 and an output circuit 13.

while the tube 11 is provided corresponding- 1y with an input circuit 14 and an output circuit 15. Output and input circuits 13 and I 14 are suitably coupled together by a device later to be described, while the input circuit 12 for the tube 10 is suitably coupled to a source of signal energy of radio frequency. Thus, a suitable absorption circuit such as a radio antenna 16 and ground 17 may be coupled to the input circuit 12 bymeans of an antenna inductance 18 which is in inductive relation to the'sccondary inductance 19 in the input circuit 12. A variable condenser 10 and 11 are preferably of the usual type having an electron emisson element 22, grid or control electrode 23 and plate or anode 24. The electron emission element is connccted-in common to the input and output circuits while the grid 23 and plate 24 are connected respectively in the input and output circuits. The electron emission elements or filaments 22 are energized from a suitable source of energy such as an A hatter 226,-.

while the respective output circuits 0 the tubes 10 and 11 are energized from a suitable source such as a B battery 27.

The circuits 13 and 14 are electrically coupled together by a suitable transformer 28. Superior resultshave been obtained by employing a transformer of the.auto-transformer type in which a single coil 29 serves as both the primary and the secondary. Thus the entire coil 29 is tuned in resonance with the frequency of the received energy by suitable means such as variable condenser 30, while one section 31 of the coil serves as a primary. The intermediate tap 32 which divides the coil 29 into two sections is electrically connected to both of the electron emission elements 22 while the other termi' nal of the section 31 is electrically connected the inductance coils 18 and 19. This shield is preferably grounded to the common filament conductor 38 as at 37.

With the arrangement shown the electron emission tubes will have a tendency to oscillate locally due to energy being fed back from the output to the input circuits. This feeding back of energy is due principally to the capaeitative coupling introduced by the grid 23 and plate 24. It may also be caused in part by capacity effects between the conductors in the input and output circuits or by a small amount of magnetic coupling between the transformer 28 and the inductance 19 in the input circuit 12. To prevent this feed-back energy from causing the tubes to oscillate locally it is necessary to impress a potential upon the grid whic is equal and opposite to the potential induced by the undesired feed-back so as to neutralize the same.- The applicant has employed an auxiliary inductance coil for this purpose,'but this coil is not magnetically coupled to eithertbe coupling transformer 28 or the inductance in the input circuit. Thus there is provided an inductance coil 40 having its one end connected electrically with the filament 22, as by means of the common filament conductor 38, and has its other end electrically connected to the grid 23 by means of the conductor 41 in series with a small variable condenser 42. For inducing a potential across the coil 40 it is preferable to employ a separate primary coil 43 having its one end electrically connected with the positive terminal of the B battery 27 as by means of the c'on ductor 44 and having its-other end electrically connected with the plate conductor 45.

1 In the particular system illustrated, the primary coil 43 serves both as a direct current ath for the B battery 27 and as a means or inducing, a potential across the coil 40. The size of the coils 40 and 43 and the degree of coupling between them may vary to suit different operating conditlons. However, it has been found preferable to construct these coils so that the resonance period of the coil 43 when coupled to coil 40 coming energy. The reactance of coil 43 will cause a'large proportion of the amplified radio frequency energy in the output circuit 13 to be transferred to the input circuit 14 of the tube 11 through the coupling transformer 28. However, a certain proportion of the high frequency energy is by-passed by the coil 43 and 'a potential is thereby induced across the coil 40. The polarity of this potential is reversed by means of the condenser 42 and impressed upon the grid 23 by means of the conductor 41 to neutralize the disturbing potential placed upon the rid 23 because .of the feed-back between t e output circuit 13 and the input circuit 12. When the system is tuned in resonance with a higher frequency the feed-back of energy between the grid 23 and plate 24 is also increased accordingly, ,as the rcactance between these electrodes decreases in proportion to the increase in frequency. -At the same time however. the inductive reactance of the coil 43 will also increase so that a higher potential will be impressed upon the grid 23 through the conductor 41. In rac tice it has been found that the feed-bac energy may not increase as the linear function of the frequency, but ma increase at a disproportionate rate. Wit this invention it is possible to neutralize such feed-back energy by constructing the coil 43 so that its inductive reactance will also vary at a disproportionate rate with the frequency. This may be accomplished byintroducing a small amount of distributive capacity between the windings of thecoil 43 so that the reactance curve for the coils 43'and 40 taken togeher will not be a straight line. B adjusting the condenser 42 or by changing the coupling between the coils 40 and 43 the neutralizing potential may be varied for any one frequency.

I claim i 1. In a radio frequency system of the class described comprising an electron emission tube having input and output circuits each being associated with other circuits thru inductive coupling devices, saidsystem having undesired feed-back of energy from the'output circuit into the input circuit, and means I moved from? inductive relation" to said couplingdevices.

2. ;I n" a radio fre uen'cy system, an electron emission tube iaving the usual grid --andplate electrodes connected to' input and plate electrodes connected to input and output circuits-respectively, inductive coupling means in each circuit for associating the same with other circuits, and means for impressing a neutralizing potential upon the input circuit to revent local oscillations, said means 'inclu 'ng .a transformer energized from the output circuit, one output terminal of the transformer being connected to the grid ofthe tube th'ru'a'capacitance, the transformer being'removed from inductive relation to the coupling means.

4. In' a radio frequency system, an electron emission tube having the usual grid and plate electrodes connected to input and output circuits res ectively,: inductive coupling means in eaci circuit for associating the sainewith other circuits, and means for impressing a neutralizing potential upon the input circuit to prevent local oscillations, said means including a transformer having primary and secondary windings, the primary being energized by energy from the output circuit, the secondary being connected to the in ut. circuit in series with a capacitance, sai windings bein coupling- 5. In a radio frequency system, an electron emission tube having the usual grid and plate electrodes connected to input and output circuits respectively and an electron emission element in common with said circuits, a source of energy for the output (Elfcuit having its negative terminal connected to said emission element, an inductance having its one end connected to the positive terminal of said source and at its other end connected to said plate to place a positive potential upon the same, a transformer for coupling sa d output circuit to another circuit, a capacitance in series with the input of said transformer, and another inductance inductively coupled to said first inductance, said latter inductance having its one end electrically connected to said emission element and'its other end connected to said removed eigy is etiected, said inductances being in su stantially non-inductive relationship to said transformer.

6. In a radio frequency system, an electron emission tube having the usual grid and plate electrodes connected to input and output circuits respectively and an electron emission element in common with said cir-V cuits, a source of energy for the output circuit having its negative terminal connected to said emission elementyan inductance having its one end connected to the positive terminal of said source and at its other end connected to said plate to place a positive potential upon the same, a transformer for coupling said output circuit to another cir- I cuit, a capacitance in series with the input of said transformer, and means for causing the field of said inductance to induce a neutralizing potential upon said grid to prevent local oscillations due to feed-back energy, said inductance being in substantially non-inductive relationship to said transformer.

7. In a radio frequency system, an electron emission tube having the usual grid and plate electrodes connected to input and output circuits respectively and an electron emission element in common with said circuits,. means for inductivelv coupling said input circuit to a source of high frequency energy, a source of energy for the output circuit havin its negative terminal connected to said emission element, an inductance having its, one' end connected to the positive terminal of said source and its other end connected to said plate to place a positive potential upon the same, a transformer for coupling the output circuit to another circuit and connected to the out at circuit in series with a capacitance, sai inductance being removed from inductive relation with both said coupling means and said transformer, and means for causing the field of said inductance to induce a neutralizing potential upon said grid to prevent local oscillations due to feeding back of energy from the output circuit into, the input circuit.

8. In a radio frequency system, an electron emission tube having the usual grid and plate electrodes connected to input and output circuits respectively and an electron emission element in common with said circuits, means for inductively coupling said input circuit to a source of high frequency energy, a source of energy for the output circuit having its negative terminal connected to said emission element, an inductance having its one end connected to the positive terminal of said source and its other end connected to said plate to-place a positive potential upon the same. a transformer for coupling the out ut circuit to another circuit and connecte to the output circuit in series with a capacitance, said inductance being removed from inductive relation with both said coupling means and said transformer, and. another inductance inductively coupled to said first inductance, said latter inductance having its one end electrically connected to said emission element and its other'end connected to said grid in series with a'capacitance, thereby effecting neutralization ot'energy fed back from said output circuit into said input circuit.

9. The method of effecting neutralization ofundesirable feed-back energy in a radio frequencysystem characterized by the use of an electron emission tube having its input and output circuits inductively coupled with other circuits, said method comprising resolving a portion of the energy in the outthe effect of feed-back energy from the output circuit into the input circuit;

In testimony whereof, I have hereunto set 25 my hand.

ROGER 'M. WISE. 

